Dynamic intervertebral implant

ABSTRACT

The implant includes two side walls resting against the vertebral end-plates and an intermediate wall joining the supporting walls. The implant can be deformed for insertion between the vertebrae to be treated to restore the attenuated mobility of the vertebrae, and includes mounting elements mounting on the vertebrae. The side walls have a curved shape, whose convexity is oriented towards the outside of the implant; the intermediate wall has a curved shape, whose convexity is oriented towards the outside of the implant such that it does not form any pronounced angles with the supporting side walls. The supporting side walls and the intermediate wall, have a partially oval shape; and the mounting elements are configured such that the implant can be mounted on the vertebrae.

The present invention relates to an intervertebral implant, notablyintended for the treatment of cervical vertebrae by anterior approachroute.

It is known to use intervertebral implants to restore the anatomicintervertebral space between two vertebrae. However, the existingimplants are not completely satisfactory, in particular as regards thetreatment of cervical vertebrae by anterior approach route, eitherbecause they do not restore perfectly the intervertebral space, orbecause they form obstacles to the movements of the vertebrae, orbecause they induce risks of insertion in the vertebral plates, orbecause they are difficult to implant, or because their durability orthe anchoring thereof is questionable.

The document U.S. Pat. No. 5,749,16 describes a fusion cage slitlaterally to enable the application of stresses on a graft contained inthe wedge and/or for restoring anatomic mobility between two vertebrae.

This implant is not intended for treating cervical vertebrae by anteriorapproach route, and the implant according to the invention does notcomprise any lateral slot.

There is also provided, by the document WO 01/62190, an intervertebralimplant comprising a U-shaped body seen laterally, i.e. showing twolateral branches resting against the vertebral plates and a posterior“wall”. This body is deformable elastically for the insertion thereofbetween the vertebrae to be treated and to enable restoration of themobility of the vertebrae, and forms protruding tabs for the attachmentthereof to the vertebrae.

This implant is estimated as not satisfactory from the point of view ofthe restoration of an intervertebral space with mobility of thevertebrae. Indeed, the screw attachment of this implant is considered asnot suitable for such a restoration, taking into account the risksinduced of a vertebral fusion by growth of the bony cells, which mayresult in immobilisation of the vertebrae. Moreover, the resistance ofthis implant to the repeated stresses transmitted by these vertebrae isconsidered as questionable.

The purpose of the present invention is to remedy these shortcomings.

Its main object consists thus in providing an intervertebral implantcapable of restoring adequate anatomic space between two vertebrae whilekeeping, in all certainty over time, the relative mobility of the twovertebrae treated.

Another object of the invention is to provide an intervertebral implantoffering perfect resistance to the repeated stresses transmitted bythese vertebrae.

The implant in question comprises, as known, two lateral walls bearingagainst the vertebral plates and an intermediate wall for connection ofthese lateral bearing walls, this implant being deformable elasticallyfor the insertion thereof between the vertebrae to be treated and toenable restoration of dampened mobility of these vertebrae, andincluding means for the assembly thereof to these vertebrae.

According to the invention,

-   -   said lateral bearing walls show, seen laterally, curved shapes        with their convexity turned to the outside of the implant;    -   said intermediate wall shows a curved shape, with its convexity        turned to the outside of the implant, and is such that it does        not form any marked angles with said lateral bearing walls,        these lateral bearing walls and this intermediate wall having        thus, seen laterally, partial oval “water drop”-like shape; and    -   the means for fastening the implant to the vertebrae are        designed to enable non rigid assembly of this implant to these        vertebrae, i.e. authorising slight deformation of the implant        with respect to the vertebrae as the latter are moving.

The curved shaped of said lateral walls enables these walls to adaptaccurately to the shape of the respective faces of the vertebral plates,thereby ensuring certain retention of the implant between the vertebrae.

Once in place, the implant does not oppose the movements of thevertebrae because of the deformability of the intermediate wall thereof;the risk of inserting the implant in the vertebral plates isconsequently vastly reduced, if not eliminated, the more so because saidlateral walls possess wide contact surfaces with the vertebral plates.

The absence of marked angles between said lateral bearing walls and saidintermediate wall enables to avoid, on the body of the implant, anyconcentration of the loads transmitted by the vertebrae at a givenlocation of this body, and enables consequently to this implant to haveperfect resistance to these loads over time.

The shape aforementioned of the body of the implant enables besidescertain deformation of the implant with respect to the vertebrae whenthe latter are moving, this deformation being not prevented by saidmeans for fastening this implant to the vertebrae and being only limitedby the latter.

This mobility prevents any risks of fusion of the intervertebral spacefurther to bony cells growing around the implant, and therefore to keeptotal mobility of the vertebrae relative to one another over time.

Preferably, said intermediate wall is so shaped as, when not deformed,to maintain said lateral bearing walls at a distance from one anotherwhich is slightly greater than the height of the intervertebral space tobe restored.

This intermediate wall is therefore slightly constrained when theimplant is placed and enables to ensure, by elastic return, slightsupport of the upper vertebra relative to the lower vertebra.

Advantageously, the implant is made simply by folding a single piece ofappropriate material, notably a sheet metal flank. The material used maybe, notably, titanium, aluminium and vanadium alloy, known as “TA6V”.

According to a preferred embodiment of the invention, said attachmentmeans of the implant to the vertebrae comprise at least one series ofribs parallel to one another, with sharp free ridges, protruding fromthe external face of the free end of a lateral bearing wall.

These ribs are intended for insertion in the anterior zone of the bodyof the adjacent vertebra.

The implant may comprise two series of ribs, the one on one of thelateral bearing walls, the other on the other lateral bearing wall. Fortreating cervical vertebrae, the implant exhibits advantageously a“lower” lateral bearing wall, i.e. bearing against the lower vertebraduring placement, with a length greater than that of the other lateralbearing wall.

The implant described above may be part of a set of implants includingat least one other intervertebral implant, intended to realise a fusionbetween the two vertebrae to be treated; this other implant, so-called“fusion” implant, has a structure similar to that of the implantdescribed above, but comprises attachment means which enable the rigidassembly thereof to the vertebrae treated.

Preferably, in such a case, said means enabling to attach the “fusion”implant comprise at least one tab integral with one of said lateralbearing walls, drilled with a reception hole of an anchoring screw, thisscrew being intended for insertion in the body of the correspondingvertebra.

Said lateral bearing walls of the “fusion” implant may exhibit surfacecoverings promoting their osteo-integration and/or comprise holes whichcommunicate the space delineated between them, with the exterior of theimplant. A bony graft may then be placed in this space.

For better understanding thereof, the invention is again described belowwith reference to the appended schematic drawing, representing for nonlimiting exemplification purposes, a possible embodiment possible of theintervertebral implant in question, and a “fusion” implant included in aset of implants also affected, said set comprising said intervertebralimplant according to the invention and said “fusion” implant.

FIG. 1 is a perspective view of the intervertebral implant in question;

FIG. 2 is a side view thereof after placement thereof;

FIG. 3 is a perspective view of said “fusion” implant, and FIG. 4 is aside view of this “fusion” implant after placement.

FIGS. 1 and 2 represent an intervertebral implant 1 for the treatment ofcervical vertebrae 10 by anterior approach route.

As it appears, the implant 1 is realised by folding a given piece ofmaterial and exhibits, seen laterally, i.e. in the sagittal plane afterimplantation, a curved shape delineating two lateral bearing walls 2 andone intermediate wall 3.

Said piece of material is a sheet flank made of titanium, aluminium andof vanadium alloy known as “TA6V”.

The lateral walls 2 show, seen laterally, domed shapes on the greatestportion of their length, the convexities thereof being turned towardsthe exterior of the implant 1. At their free end zones, these lateralbearing walls 2 are rectilinear in shape and comprise each a series ofribs 4.

The length of the “lower” wall 2, i.e. abutting the lower vertebraduring implantation, is greater than that of the other wall 2.

The intermediate wall 3 has a curved shape whereof the convexity isturned towards the exterior of the implant. As appears clearly, it doesnot form any marked angles with the lateral bearing walls 2, theselateral bearing walls 2 and this intermediate wall 3 having thus, seenlaterally, partially oval “water drop’-like shape.

The intermediate wall 3 is moreover deformable elastically between aneutral form, wherein it maintains normally the walls 2 at a distancefrom one another which is slightly greater than the height of theintervertebral space to be restored, and a constrained shape, whereinsaid wall 3 enables to bring the free ends of both walls 2 together.This bringing together is such that it enables to reduce the height ofthe implant 1 so that such height is smaller than the height of theintervertebral space to be restored.

The ribs 4 are parallel to one another and protrude from the free endzone of each wall 2, towards the exterior of the implant 1. Each of themis delineated by an anterior face perpendicular to the longitudinaldirection of the implant 1 and by a tilted posterior face, forming anangle of approximately 500 with the anterior face. These ribs 4 thusexhibit relatively sharp free ridges.

The implant 1 represented for exemplification purposes exhibits thefollowing dimensions:

-   -   maximum dimension of the implant in the sagittal plane:        approximately 17 mm;    -   difference in length of the walls 2: approximately 1 mm;    -   dimension of the implant in the front plane: approximately 18        mm;    -   thickness of said flank at the walls 2 and of the wall 3:        approximately 1 mm;    -   maximum thickness of the implant 1, at the exterior domed faces        of the lateral walls 2: approximately 7 mm;    -   curvature radius of the upper half of the intermediate wall 3:        approximately 2.7 mm;    -   curvature radius of the lower half of the intermediate wall 3:        approximately 3.3 mm;    -   curvature radius of the domed zone of the upper lateral wall 2:        10 mm;    -   curvature radius of the domed zone of the lower lateral wall 2:        approximately 25 mm.

In practice, the walls 2 are brought towards one another by deformationof the wall 3, to enable insertion of the implant 1 between thevertebral plates of the two vertebrae 10 to be treated, then, once saidinsertion is completed, the walls 2 are released, which presses saidwalls against these vertebral plates. The ribs 4 are inserted in thevertebral plates and enable non rigid assembly of the implant 1 to thesevertebrae or tissues, i.e. allowing slight deformation of the implantwith respect to the vertebrae as the vertebrae are moving, whileopposing any expulsion of the implant.

The domed shape of the walls 2 enables these walls to match preciselythe shape exhibited by the respective faces of these vertebral plates,and ensures certain retention of the implant between the vertebrae 10.The elastic stress remaining in the wall 3 enables to maintain the ribs4 inserted in the vertebrae 10.

The “fusion” implant 11 shown on FIGS. 3 and 4 have a structure similarto that of the implant 1 described above, except that the walls 2comprise two tabs 5, interconnected therewith and extend their freeends.

Each of these tabs 5 is attached to the end of the wall 2 which supportsthe latter by two curved lateral connection zones, which enable toensure perfectly solid link of this tab 5 and of the wall 2, and isdrilled with a hole accommodating an anchoring screw 6. This screw 6 isintended to be inserted in the body of the corresponding vertebra 10, asshown on FIG. 4.

Each tab 5 forms an angle of the order of 120° with the generalantero-posterior direction of the wall 2 to which said tab is attached,and exhibits a thickness greater than that of the remainder of theimplant 1. This thickness is approximately 1.5 mm in the examplerepresented.

The “fusion” implant 11 is used to realise a fusion between the twovertebrae 10 to be treated.

It appears from the foregoing that the invention brings a decisiveimprovement to the anterior technique, by providing an intervertebralimplant enabling perfect restoration of the intervertebral space,without opposing the movements of the vertebrae, without inducing anyrisks of insertion in the vertebral plates nor of risk of fusion bygrowing bony cells, while being easy to be implanted and whereof thedurability is not questionable.

It goes without saying that the invention is not limited to theembodiment described above for exemplification purposes, but it includesconversely all the embodiment variations covered by the appended claims.

1. Intervertebral implant (1), notably intended for the treatment ofcervical vertebrae (10) by anterior approach route, comprising twolateral walls (2) bearing against the vertebral plates and anintermediate wall (3) for connection of these lateral bearing walls,this implant (1) being deformable elastically for the insertion thereofbetween the vertebrae (10) to be treated and to enable restoration ofdampened mobility of these vertebrae (10), and including means (4) forthe assembly thereof to these vertebrae (10); Implant (1) characterizedin that: said lateral bearing walls (2) show, seen laterally, curvedshapes with their convexity turned to the outside of the implant (1);said intermediate wall (3) shows a curved shape, with its convexityturned to the outside of the implant (1), and is such that it does notform any marked angles with said lateral bearing walls (2), theselateral bearing walls (2) and this intermediate wall (3) having thus,seen laterally, partial oval “water drop”-like shape; and the means (4)for fastening the implant (1) to the vertebrae (10) are designed toenable non rigid assembly of this implant (1) to these vertebrae (10),i.e. authorising slight deformation of the implant (1) with respect tothe vertebrae (10) as the latter are moving.
 2. Implant (1) according toclaim 1, characterized in that said intermediate wall (3) is so shapedas, when not deformed, to maintain said lateral bearing walls (2) at adistance from one another which is slightly greater than the height ofthe intervertebral space to be restored.
 3. Implant (1) according toclaim 1, characterized in that the implant (1) is made simply by foldinga single piece of appropriate material, notably a sheet metal flank. 4.Implant (1) according to claim 3, characterized in that the materialused is the titanium, aluminium and vanadium alloy known as “TA6V”. 5.Implant (1) according to claim 1, characterized in that said attachmentmeans of the implant (1) to the vertebrae (10) comprise at least oneseries of ribs (4) parallel to one another, with sharp free ridges,protruding from the external face of the free end of a lateral bearingwall (2).
 6. Implant (1) according to claim 5, characterized in that itcomprises two series of ribs (4), the one on one of the lateral bearingwalls (2), the other on the other lateral bearing wall (2), and in thatit exhibits a “lower” lateral bearing wall (2), i.e. bearing against thelower vertebra during placement, with a length greater than that of theother lateral bearing wall (2).
 7. Set of intervertebral implantscomprising at least one intervertebral implant (1) according to claim 1,characterized in that it comprises at least one other intervertebralimplant (11), intended to realise a fusion between the two vertebrae(10) to be treated; this other implant (11), so-called “fusion” implant,has a structure similar to that of the implant (1) described above, butcomprises attachment means which enable the rigid assembly thereof tothe vertebrae (10) treated.
 8. Set of implants according to claim 7,characterized in that said means enabling to attach the “fusion” implant(11) comprise at least one tab (5) integral with one of said lateralbearing walls (2), drilled with a reception hole of an anchoring screw(6), this screw (6) being intended for insertion in the body of thecorresponding vertebra (10).
 9. Set of implants according to claim 7,characterized in that said lateral bearing walls (2) of the “fusion”implant (11) exhibit surface coverings promoting their osteo-integrationand/or comprise holes which communicate the space delineated betweenthem, with the exterior of the implant (1).
 10. Set of implants (1)according to claim 9, characterized in that the “fusion” implant (11)receives a bony graft placed in the space delineated between saidlateral bearing walls (2).
 11. Implant (1) according to claim 2,characterized in that the implant (1) is made simply by folding a singlepiece of appropriate material, notably a sheet metal flank.
 12. Set ofimplants according to claim 8, characterized in that said lateralbearing walls (2) of the “fusion” implant (11) exhibit surface coveringspromoting their osteo-integration and/or comprise holes whichcommunicate the space delineated between them, with the exterior of theimplant (1).